1. Field of the Invention
The present invention relates to ground water sampling devices of the general type shown in U.S. Pat. No. 4,717,473 to Burge, et al. The present invention relates more particularly to a seal structure usable on the sampling unit to prevent exchange of atmospheric gases with the sub-surface ground water.
2. Prior Art
U.S. Pat. No. 4,717,473 discloses a ground water sampler device lowerable into a well casing for collecting samples of sub-surface ground water in the well casing. The sampler device has an annular elastomeric sealing sleeve inflatable to sealably engage the casing wall, to prevent the sampled ground water from being contaminated or altered by contact with above-ground atmospheric gases. The elastomeric sealing sleeve is pressurized by compressed air through a small diameter hose extending from the round surface to the sampling unit. The sealing sleeve is required to be pressurized in order to seal against the well casing. Should the air pressure be lost for any reason, the sealing sleeve will be depressurized and will move out of sealing engagement with the well casing. In some cases the sampling unit remains in the well casing for several months, and the sealing sleeve on the sampling unit is therefore required to remain in a pressurized state for the entire period of time that the sampling unit is in the well casing. The long period of seal pressurization increases the probability of seal failure by pressure loss. Also, the continuous pressurization forces tend to unduly stress the seal material because such forces are exerted on the seal material for prolonged time periods.